Experiments will be continued which are designed to elucidate the mechanisms of synaptic interaction and neurotransmitter sensitivities of tuberal hypothalamic neurons in tissue culture. By using focal electrical or drug stimulation, it is possible to selectively excite one neuron or a small set of neurons in a culture, and ascertain the effects of these stimuli on the activity of other nearby neurons. The effects of peptide hormones and steroids will also be investigated. Quantification of these effects is made possible through the use of an on-line Nova 2/10 digital computer. The computer is programmed to accept unit responses, and to create interspike and post stimulus and post drug interval histograms. These histograms are displayed during data collection and are stored on discs for further analysis. In related experiments, we are using biochemical and histochemical techniques to study the intracellular mechanisms of response to hormones of cells of the cultured hypothalamus. The primary question is to determine the role of second messengers in the function of the tuberal hypothalamus. Likely candidates for second messengers in this system include cyclic AMP and calcium, and ways are being explored to connect changes in levels of these substances with physiological events. The biochemical effects of other substances which affect the tuberal hypothalamus, such as peptide and steroid hormones, are also being investigated. BIBLIOGRAPHIC REFERENCE: Geller, H.M., Phasic discharge of neurons in long-term cultures of tuberal hypothalamus. Brain Research, "93," 511 (1975).